Field of The Invention
The invention relates to a method for locating an earthbound and freely movable vehicle, said method comprising the steps of:
in said vehicle interfacing to an external coordinate system for determining an actual position of the vehicle, PA0 and via wireless means transmitting said position on a recurrent basis to a remote station. PA0 The most common example of such vehicle is a motor car in its various embodiments. The invention does not relate to robotic vehicles, to aeroplanes or to rail vehicles, for which often the motion of a single vehicle determines which direct control measures must be taken by the central station to influence the movement of the object. Moreover, these vehicles are not freely movable, but must necessarily follow specified paths in space and time. Robots must perform tasks that are specified minituously. Aeroplanes usually follow continual directions from flight control. Rail vehicles are bound to rails and follow tight schedules. In contradistinction, in the environment of the present invention the central or remote station is not able to follow the vehicle by means of direct sighting through camera, radar or the like, and in principle, the vehicle is independent. The present invention relates to an environment where either the central station is active in tracking-only of the positions, or where it executes only global measures. In this way, the actual position as communicated to the central station can be used for various purposes. Examples are planning of the overall moving of a fleet of service vehicles such as taxis, or the assigning of particular road facilities to appropriate traffic streams. In case the vehicle would deviate from a planned route, the central station could assign a warning or control a change of facilities for receiving the vehicle.
Various methods have been published for determining the actual position of the vehicle. A first method operates with beacons that transmit an actual site code to the vehicle when passing. A second method operates with the so-called GPS or Global Positioning System that through reception of satellite-transmitted wave patterns is able to calculate an actual vehicle position. A third method determines the position exclusively thru in-vehicle sensors, such as odometer and compass. A fourth method determines the position through so-called dead reckoning in comparison to a known road pattern that is retrieved from a mass memory within the vehicle or otherwise. Various combinations of the above methods have attained better accuracy or robustness against interferences or against measuring errors.
One method for transmitting the actual vehicle position to the central station is with a fixed recurrence period. When the number of vehicles is small, this is particularly advantageous, because the central station can actually predict when the next message will arrive, and through some policy for time slot assignment make the best of its limited reception facilities. However, when the number of vehicles grows, and also when their assignment becomes dynamic to various central stations that are organized on a cellular basis, the present inventor has concluded that the number of such transmissions should be advantageously kept low by suppressing the transmitting when effectively no relevant information can be gathered. A further aspect is cost, when some governing authority would tax either the operator of either the vehicle or of the central station for each transmission: when fixed, the transmission recurrency is kept relatively high to cater for the most exacting situation.